The present invention relates to a variable displacement swash plate type compressor, in which pistons engaged with a swash plate are reciprocated by a stroke corresponding to the inclination angle of the swash plate.
Generally, when the pressure in a control pressure chamber of a variable displacement swash plate type compressor increases and approaches the pressure of the discharge pressure zone, the inclination angle of the swash plate decreases. This reduces the stroke of the pistons, and the displacement is decreased, accordingly. In contrast, when the pressure in a control pressure chamber decreases and approaches the pressure of the suction pressure zone, the inclination angle of the swash plate increases. This increases the stroke of the pistons, and the displacement is increased, accordingly. The variable displacement swash plate type compressor includes a displacement control valve. The displacement control valve controls the pressure in the control pressure chamber.
For example, Japanese Laid-Open Patent Publication No. 52-131204 discloses a compressor having a movable body that moves along the axis of the rotary shaft to change the inclination angle of the swash plate. As control gas is introduced to the control pressure chamber in the housing, the pressure inside the control pressure chamber is changed. This moves the movable body along the axis of the rotary shaft. As the movable body is moved along the axis of the rotary shaft, the movable body applies to a central portion of the swash plate a force that changes the inclination angle of the swash plate. As a result, the inclination angle of the swash plate is changed. Since the control pressure chamber is a small space compared to the swash plate chamber, only a small amount of refrigerant gas needs to be introduced to the control pressure chamber. This improves the response of change in the inclination angle of the swash plate. As a result, the inclination angle of the swash plate is smoothly changed, and the amount of refrigerant gas introduced to the inside of the control pressure chamber is not unnecessarily increased.
The swash plate has a top-dead-center corresponding part, which puts pistons at the top dead center.
Consideration will now be given to a structure for transmitting force that changes the inclination angle of a swash plate from a movable body to a part of the swash plate that is close to the top-dead-center corresponding part for the pistons. According to this configuration, if the range of changes in the inclination angle of the swash plate is the same, the movement distance of the movable body along the axis of the rotary shaft when the inclination angle of the swash plate is changed is small compared to the compressor of the above mentioned publication, in which the force that changes the inclination angle of the swash plate is transmitted from the movable body to the central part of the swash plate. This allows the axial size of the variable displacement swash plate type compressor to be reduced.
However, in the configuration in which the movable body applies a force for changing the inclination angle of the swash plate to the part of the swash plate that is close to the top-dead-center corresponding part for the pistons, a change in the inclination angle of the swash plate causes the movable body to receive a moment that acts to tilt the movable body with respect to the moving direction. If the movable body tilts with respect to the moving direction, a force that supports the tilting motion of the movable body is generated between the movable body and the rotary shaft while the movable body and the rotary shaft are contacting each other at two contact points on the opposite sides of the rotary shaft. The friction caused by the force generates a twist between the movable body and the rotary shaft. The twist increases the sliding resistance, hindering smooth movement of the movable body along the axis of the rotary shaft. This hampers smooth change in the inclination angle of the swash plate.